In recent years, with the increase in integration of semiconductors, a material for use in a gate insulating film of a MIS transistor has been shifted from SiO2, obtained by oxidizing a conventional silicon substrate (Si substrate), to a material (high-k) having a larger dielectric constant. However, there are problems with the high-k material in that the dielectric constant of the high-k material decreases due to mutual diffusion of the high-k material and the Si substrate, and further, the diffusion layer increases due to heat treatment performed in the transistor production process.
In order to solve the problems as described above, for example, a technique has been proposed which is described in Japanese Patent Laid-Open No. 2002-43565. This is a technique in which a Si3N4 film obtained by nitriding Si is once formed on a Si substrate and then a high-k film is formed so that the mutual diffusion of the Si substrate and the high-k material can be prevented.
However, in the technique described in the above-mentioned publication, there has occurred a problem of deterioration in transistor characteristics due to the existence of nitrogen in the vicinity of the Si interface, and this has prevented certain production of a high-quality MIS transistor.
The present invention was made, taking note of the foregoing matters, and has an object to provide a high-quality semiconductor device in which deterioration in transistor characteristics and an increase in interface layer due to a gate insulating film are suppressed, and a method for manufacturing the same.